1. Field of the Invention
The present invention generally relates to an engaging member and a packing bag with an engaging member, and particularly to an engaging member and a packing bag with an engaging member which can be applied to packaging in the field which requires moisture prevention, oxygen-blocking property, and having a function that it can be sealed again after it is opened, such as foods, medicine, and miscellaneous goods.
2. Description of the Related Art
A bag for packing having an engaging member (zipper bag) consisting of a male part and a female part which enables the bag to be opened and closed freely is used in various fields, such as food, medicine, and miscellaneous goods. As for the process for producing such a packing bag with an engaging member, various processes are proposed. For example, a method of integrally extruding a cylindrical film having a pair of engaging member consisting of a male mold and a female mold through a circular die, a method of extruding and welding an engaging members onto a film, and a method of thermally welding an engaging member which is prepared beforehand onto a base material film as a main body of a packing bag or fixing such an engaging member to the base material film using an adhesive.
However, each of the former two methods has problems in handling and cost, for example, the kind of resin which can be used is restricted, it is difficult to apply the method to a multi-layered film substrate, it is difficult to apply the method to bags having various size, and printing on the bag is difficult, and hence, the method of thermally welding the engaging member prepared beforehand onto a base material film as a main body of a packing bag is used generally.
As the material for preparing the engaging member, polyethylene type resin and polypropylene type resin are widely used, and in the case in which the material of the welded part of the engaging member is a polypropylene type resin, as a base material film of the main body which is thermally welded, laminate films, such as OPP/CPP (oriented polypropylene/non-oriented polypropylene), ONy/CPP (oriented nylon/non-oriented polypropylene), PET/CPP (oriented polyester/non-oriented polypropylene), etc., are used, and among these, OPP/CPP is exemplary as a general-purpose base material film.
In the case of OPP/CPP which is a general-purpose base material film, both the welded layer and non-welded layer of the base material film are made of a polypropylene type resin, the temperature difference between the welded layer and the non-welded layer is small, compared with that of the base material film such as ONy/CPP, PET/CPP, etc., and as a result, if the welding temperature when when welding the welding part of the engaging member with the base material film is high, then it affects on the non-welded layer side, thereby generating external defects on the bag such as shrinking, creases, etc. On the other hand, if the welding temperature when welding the welding part of the engaging member with the base material film is low, then it takes a long time for welding, bag producing speed, that is, the productivity will deteriorate, and in addition, the energy cost will increase.
Accordingly, an engaging member which is capable of being welded with the base material film at a lower temperature and has a basic performance as an engaging member is required from the view-point of improvement of production efficiency, energy-saving, and improvement of external appearance. Under such circumstances, for example, Patent document 1 (Japanese Unexamined Patent Application, First Publication No. H08-192858) discloses a polypropylene type engaging member made of a crystalline propylene-ethylene-butene-1 random terpolymer, and an engaging member formed by a mixture consisting of not less than 60 weight % of a crystalline propylene-ethylene-butene-1 random terpolymer and not more than 40 weight % of an ethylene-butene-1 copolymer and/or low density polyethylene.
However, if an engaging member is formed by a crystalline propylene-ethylene-butene-1 random terpolymer, then sufficient welding ability at a low temperature is not obtained, although the welding ability at a low temperature is improved. On the other hand, if a polyethylene type resin is blended, although the welding ability at a low temperature is inclined to be improved, then no satisfactory performance can be obtained, because the polypropylene type resin and the polyethylene type resin are different in nature to each other, and hence commercial value deteriorates due to external defects caused by problems such as incompatibility therebetween, etc.
Thus, it is an object of the present invention to provide an engaging member having a sufficient welding ability at a low temperature and satisfactory external appearance, and a packing bag with such an engaging member.